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ARS Home » Pacific West Area » Wapato, Washington » Temperate Tree Fruit and Vegetable Research » Research » Publications at this Location » Publication #436797
Research Project: New Technologies and Approaches for Managing Insect, Nematode, and Microbial Pests of Potatoes

Location: Temperate Tree Fruit and Vegetable Research

Title: Antimicrobial peptides expressed by plant-engineered ‘symbiont’ technology reduces titers and disease symptoms of “Candidatus Liberibacter solanacearum” in potato

Author
item Cooper, William
item FLEITES, LAURA - Agrosource, Inc
item Shatters, Robert
item Pitino, Marco
item CORADETTI, SAMUEL - Boyce Thompson Institute
item HECK, MICHELLE - Virginia Polytechnic Institution & State University

Submitted to: bioRxiv
Publication Type: Pre-print Publication
Publication Acceptance Date: 8/7/2026
Publication Date: 8/10/2026
Citation: Cooper, W.R., Fleites, L.A., Shatters, R.G., Pitino, M., Coradetti, S., Heck, M. 2026. Antimicrobial peptides expressed by plant-engineered ‘symbiont’ technology reduces titers and disease symptoms of “Candidatus Liberibacter solanacearum” in potato. bioRxiv. https://doi.org/10.64898/2026.08.07.743526.
DOI: https://doi.org/10.64898/2026.08.07.743526

Interpretive Summary: A novel plant bioengineering approach known as the “symbiont” concept was recently developed, offering the ability to alter plant traits without modifying the plant’s underlying genotype. Researchers at USDA ARS in Wapato, Washington and Ithaca, New York, together with the Boyce Thompson Institute, evaluated whether symbionts engineered to produce antimicrobial peptides could protect potato plants from Liberibacter solanacearum, the causal agent of zebra chip disease. Their results showed that two such peptides significantly reduced both the abundance and movement of the pathogen within potato plants. This work provides the first demonstrated case of altering plant phenotypes through the symbiont engineering concept. The findings open new opportunities for using symbionts to address challenging vascular diseases such as citrus greening, cherry X disease, and other fastidious plant pathogens.

Technical Abstract: Delivery of therapeutic biomolecules into plant vascular tissues remains a challenge in management of vector-borne plant pathogens. The symbiont concept uses reprogrammed Agrobacterium tumefaciens galls (called symbionts) to produce biomolecules while remaining connected to host vasculature. We evaluated whether symbionts expressing antimicrobial peptides (AMPs) suppress ‘Candidatus Liberibacter solanacearum’ (CLso), the causal agent of potato zebra chip disease. Symbionts were engineered to express a Streptococcus mutans bacteriocin associated with bacterial membrane disruption (Blp-Sm), or an AMP isolated from finger lime and associated with resistance to citrus greening disease (MaSAMP). Effects of AMP-producing symbionts on CLso titers, infection incidence, pathogen movement, and disease symptoms were evaluated in tomato and potato. In tomato, neither AMP significantly reduced CLso titers or infection incidence. However, in potato, AMP-producing symbionts reduced CLso accumulation and movement from CLso-inoculated source shoots into non-inoculated sink shoots connected through underground tubers. Blp-Sm produced the strongest reduction in CLso accumulation and infection incidence in sink tissues. In separate assays where symbionts were established directly on potato seed tubers, MaSAMP significantly reduced CLso titers in stems and tubers and reduced zebra chip symptoms in tubers, despite no reduction of CLso titers in terminal leaves. These findings demonstrate that AMP-producing symbionts suppress vascular pathogen accumulation and movement within plants and highlight the symbiont concept as a potential platform for managing diseases caused by vascular-restricted pathogens. Further, they show the potato-CLso system is a promising infection model to both refine and improve symbiont technology, and to test additional AMPs for potency against related pathogens.